1. Field of the Invention
The present invention relates to an antenna and a wireless IC device. Specifically, the present invention relates to a loop-shaped antenna and a wireless IC device equipped therewith.
2. Description of the Related Art
As the structure of an antenna provided in a wireless tag, a loop antenna is known. In general, the loop antenna is configured using an electrode (conductor) formed in a loop shape beginning at a feeding point. A loop antenna is disclosed in “Antenna Engineering Handbook”, written and edited by The Institute of Electronics and Communication Engineers, published by Ohmsha, Ltd., Mar. 5, 1999, P. 20 to P. 22.
However, since, in general, the loop antenna has an impedance whose real portion is small, there has been a problem that it is hard to achieve impedance matching with a wireless IC and a gain is easily deteriorated. Namely, while the real portion of the impedance of the wireless IC is within the range of 10Ω to 20Ω, for example, the real portion of the impedance of the loop antenna is as low as 5Ω, for example.
The above-mentioned problem is especially noticeable in a UHF frequency band, and the problem grows bigger in a wireless tag utilizing a UHF band.